1. Field of the Invention
The present invention relates to sharpening devices for edge tools such as chisels, gouges, planer blades, and the like.
2. Brief Description of the Prior Art
Sharpening devices and methods for tools date from prehistory. In modern times edge tools such as chisels are manufactured from hardened, tempered steel and have edges that can be sharpened by grinding with a suitable abrasive material or stone. While sharpening can be carried out be hand, by drawing the tool edge across the face of a stone, in a production environment it is easier to keep the tool edge fixed and move the stone. A conventional grinding apparatus employs a circular abrasive wheel rotated at constant angular speed by an electric motor. The wheel can be formed with a cylindrical peripheral surface parallel the axis of rotation, and the operator moves the tool edge into contact with the peripheral surface of the rotating wheel. Conventionally, the wheel is mounted vertically so that it rotates about a horizontal axis, and the operator move the tool in a generally horizontal plane.
The circular wheel provides a hollow grind. Often it is desirable, however, to provide a flat grind on the tool edge. This geometry provides a more durable, longer lasting edge. This can be accomplished by drawing the tool edge over a flat stone surface by hand. Alternatively, a rotating abrasive cup wheel or abrasive disk can be used. Human ergonomics and convention suggest that in this instance the abrasive wheel preferably rotate in a horizontal plane, and that the tool be moved into contact with the upper surface of the rotating wheel, in a generally horizontal plane.
Conventionally, grinding and honing form two distinct and successive stages in the preparation of the tool for use. Grinding consists of imparting the required geometry or shape to the cutting part of the tool. Next, honing consists of refining the leading or cutting edge so that it exhibits a high degree of sharpness. These two stages often require sharpening stones with different geometries (whether hand or powered) and made of different grades of abrasive. Hence more than one sharpening device may be employed to fully prepare the tool.
U.S. Pat. No. 6,676,495 discloses a powered sharpening system in which a generally horizontal turntable is used to rotate reversible, interchangeable platters carrying different grades of abrasive for grinding, polishing, and lapping woodworking and other edge tools. A belt and vertically mounted conventional sharpening wheel are also provided and driven by the same electric motor.
Grinding steel on an abrasive produces frictional heat. When sharpening is accomplished by hand, the frictional heat produced is likely dissipated on a time scale comparable to its generation and there is no significant heat build up. However, when the stone is driven mechanically, significant heat can be generated at a rate faster than dissipation, raising the temperature of both the stone and the work piece being sharpened. This is undesirable, because the tool is frequently a tempered steel, which can lose its temper if a critical temperature is exceed, hence weakening the tool.
Mechanical grinders can be provided with a cooling bath, such as a water-filled trough in which the wheel is partially submerged.
There is a need for a versatile sharpening device for edge tools that can provide a single sharpening wheel in either a vertical or horizontal orientation, while also maintaining the wheel in contact with a cooling fluid.